In a conventional package-On-package (POP) process, a top package, in which a device die is included, is bonded to a bottom package. The bottom package may also have a device die packaged therein. By adopting the PoP process, the integration level of the packages is increased.
In some existing PoP processes, a bottom package and a top package are formed first, and are then bonded to each other through solder balls. A molding compound is then filled into the space between the top package and the bottom package, so that the top package and the bottom package form a rigid structure.